The present invention relates to a disk driving apparatus for driving a disk mounted therein.
Conventionally, a disk driving apparatus for driving a disk as a recording medium uses a brushless three-phase motor (hereinafter also referred to simply as a “motor”) without a Hall device for detecting a rotational position. A counter-electromotive voltage of each phase obtained by rotation of the motor is compared with a voltage at a central point CP of the motor to generate a signal determining a result of the comparison, and the signal is delayed by a predetermined time, whereby the phase of the motor is switched.
In such a method, when a counter-electromotive edge is not detected due to a disturbance to the rotation of the motor or a sudden change in the rotational speed of the motor, or when a spike noise occurring at the time of phase switching is detected erroneously as a counter-electromotive edge signal, it is not possible to control the motor properly.
In order to solve such a problem, a method has been proposed which interpolates a counter-electromotive edge signal in an analog manner by a PLL circuit using a voltage-controlled oscillator.
However, the method of controlling a counter-electromotive edge signal by the analog PLL circuit requires a voltage-controlled oscillator, as mentioned above. Therefore, the number of external components, the number of pins required of an LSI and the like are increased, which results in an increase in the cost of manufacturing.
In addition, such a control method requires a low-pass filter included in the analog PLL circuit to be adjusted by hardware means. It is therefore difficult to optimize control of the motor.
Furthermore, the characteristics of the above-mentioned voltage-controlled oscillator may vary greatly when the voltage-controlled oscillator is mass-produced. Therefore, when the voltage-controlled oscillator is included in a motor driver IC, the voltage-controlled oscillator can be a factor in an decrease in the yield of the motor driver IC.